Technical Field
The present disclosure relates to a laser gas analyzer that can efficiently measure a hydrocarbon multicomponent mixed gas in which multiple hydrocarbon components are mixed.
Related Art
A laser gas analyzer using tunable diode laser absorption spectroscopy (TDLAS) method has an advantage of a capability of measuring the concentration of a measurement subject component such as a high-temperature or corrosive gas in a highly component-selective, non-contact, and fast manner on a real time basis without interference by other components simply by irradiating light to a measurement subject from a wavelength-variable semiconductor laser.
FIG. 19 is a block diagram showing an example of a laser gas analyzer of the related art using the TDLAS method, and the laser gas analyzer includes a light source unit including a semiconductor laser that irradiates measurement laser light toward a measurement gas atmosphere, a light-receiving element that detects the measurement laser light which has penetrated through a measurement space of the measurement gas atmosphere, and a detecting unit including a computation processing module that processes output signals of the light-receiving element.
The laser gas analyzer shown in FIG. 19 measures the intrinsic molecular optical absorption spectrums caused by the vibrational and rotational energy transitions of measurement subject component molecules present in an infrared to near infrared range using a semiconductor laser having an extremely narrow oscillation wavelength spectrum line width. The molecular absorption spectrums of most molecules such as O2, NH3, H2O, CO, and CO2 are present in an infrared to near infrared range, and the concentration of a subject component can be computed by measuring the optical absorption amount (absorbance) at a specific wavelength.
In FIG. 19, a semiconductor laser 11 provided in a light source unit 10 irradiates a measurement laser light to the atmosphere of a measurement gas 20. Since the laser light that the semiconductor laser 11 outputs has an extremely narrow oscillation wavelength spectrum line width, and can change the oscillation wavelength by changing the laser temperature or driving current, only one of the respective absorption peaks of the absorption spectrum can be measured.
Therefore, an absorption peak not influenced by an interfering gas can be selected, the wavelength selectivity is high, and there is no influence of other interfering components, and therefore a process gas can be directly measured without removing the interfering gas in a step prior to measurement.
An accurate spectrum that does not overlap with the interfering components can be measured by scanning the oscillation wavelength of the semiconductor laser 11 in the vicinity of one absorption line of the measurement component, but the spectrum shape changes due to a broadening phenomenon of the spectrum which is caused by the measurement gas temperature, the measurement gas pressure, coexisting gas components, and the like. Therefore, in an actual process measurement accompanied by environment changes, correction for the changes is required.
Therefore, the apparatus of FIG. 19 uses a spectrum area method in which the spectrum area is obtained by scanning the oscillation wavelength of the semiconductor laser 11 and measuring the absorption spectrum, and the spectrum area is converted into the component concentration.
Other laser gas analyzers use a peak height method in which a measurement component is obtained from the peak height of an absorption spectrum, or a 2f method in which a wavelength scanning signal is modulated and the concentration of a measurement component is obtained from the peak to peak (P-P) value of the doubled frequency-modulated wave form of the frequency. However, theses methods are liable to be significantly influenced by changes in temperature, pressure, coexisting gas components, and the like.
In contrast, in principle, the spectrum area is not influenced by changes due to the difference of coexisting gas components (the spectrum area is almost constant regardless of the coexisting gas components), and the spectrum area, in principle, also linearly changes with respect to a pressure change.
In the peak height method or the 2f method, the above three factors causing change (temperature, pressure, and coexisting gas components) all have a non-linear influence, and, in a case in which the factors causing change coexist, correction is difficult. However, according to the spectrum area method, linear correction with respect to a gas pressure change and nonlinear correction with respect to a gas temperature change are possible, and accurate correction can be realized.
The measurement laser light that has penetrated through the atmosphere of the measurement gas 20 is received by the light-receiving element 31 provided in a detecting unit 30, and is converted into an electrical signal.
The output signals of the light-receiving element 31 are adjusted to an appropriate amplitude level through a gain-variable amplifier 32, inputted to an A/D convertor 33, and converted into digital signals.
The output data of the A/D convertor 33 are subjected to repetition of a predetermined number (for example, several hundreds to several thousands of times) of integration between an integrator 34 and a memory 35 and storage in the memory 35 in synchronization with scanning of the wavelength of the semiconductor laser 11 so as to remove noise included in measurement signals, and the data are flattened, and then, inputted to a CPU 36.
The CPU 36 performs a computation processing such as the concentration analysis of the measurement gas based on the measurement signals from which noise is removed, and performs the gain adjustment of the amplifier 32 in a case in which the amplitude level of the output signal of the light-receiving element 31 is not appropriate as the input level of the A/D convertor 33.
Non Patent Document 1 describes the measurement principle, features, and specific measurement examples of laser gas analysis to which wavelength-variable semiconductor laser spectroscopy is applied.